THE PEAR THRIPS IN CALIFORNIA. 51 



SEASONAL HISTORY. 



Adult thrips first appear in early February upon the fruit buds 

 and continue to emerge until in the early part of April, appearing in 

 maximum numbers from February 22 to March 10, thus covering the 

 entire period of swelling of buds and blossoming of trees. By the 

 time the fruit buds have swollen sufficiently to separate slightly the 

 bud scales at the tip the adults force their way within, feeding upon 

 the tenderest parts of the buds. Egg laying usually begins when the 

 first leaf surface or fruit stems are exposed, depending somewhat upon 

 the variety of fruit attacked. First oviposition usually occurs the 

 latter part of February and the last toward the middle of April, while 

 maximum oviposition occurs from about March 10 to April 1. The 

 majority of eggs are deposited in the fruit stems, young fruit, and leaf 

 stems, and require from 4 to 16 days to hatch, averaging about 8 days. 



By the time Bartlett pear and French prune trees are breaking 

 into full bloom the adult thrips have done practically all of the injury 

 they are able to accomplish. Injury by adult thrips is distinctly 

 associated with the fruit buds before blossoming. 



Larvae first appear in numbers toward the latter part of March and 

 can be found upon the trees up to the middle of May. They appear 

 in maximum numbers from April 1 to April 15. 



The larvae feed upon the foliage and young fruit, causing on the 

 latter the well-known thrips scab, and individuals remain on the 

 trees for two to three weeks in attaining their growth, the entire 

 brood of larvae requiring 8 to 10 weeks from the first-appearing to the 

 las t-dis appearing individuals . 



All of the larvae have dropped from the trees by the middle of May 

 and penetrated the soil to a depth of from 1 to 26 inches, depending 

 upon the type and condition of same, in most cases the majority 

 being within 8 to 9 inches of the surface. 



Sometimes in July a few larvae transform into the tender pupae, 

 and by October the pupae are in maximum numbers, the last larvae 

 pupating in November. The pupal stage lasts from one to four 

 months, the usual time being about two months. 



Early in February adults, which, in some instances, have remained 

 as such for several months in the ground, appear upon the trees and 

 wait for the first opening of buds, when they begin the work of 

 destruction. 



NATURAL ENEMIES. 



Probably no single order of insects of such great economic impor- 

 tance has so few effective natural enemies as the Thysanoptera. 

 This is partly due to the small size of the insects belonging to this 

 order, their manner of working, their great activity, their unique life 

 history, and the fact that not more than six or seven species in the 

 order have ever accomplished any great economic damage. Practi- 





